I am currently reading a paper by Cass Everitt on shadow mapping and I have one question. In the paper, there is an equation for calculating the texture coordinates like so:
[s, t, r, q] = S P L M[xo, yo, zo, wo]

s, t, r, q are the texture coords
xo, yo, zo, wo are the coords given in object space
M is the matrix that transforms from object to world space
L transforms from world to light space
P is the projection matrix for the light source
S is the scale-bias matrix, but what exactly does it do? It is given as